The present invention is directed to water-inactivatable pressure-sensitive adhesives.
It is generally recognized that liquids are effective in reducing the adhesion to skin of pressure-sensitive adhesives, especially in the form as employed in adhesive medical devices. Liquids manifest their effect in several ways such as (1) interaction with the adhesive mass so as to alter the viscoelastic properties of the adhesive resulting in adhesive and/or cohesive failure, or (2) by disrupting the skin/adhesive contact interface. Rarely, although occasionally, the liquid acts upon the interface between the adhesive and any backing support employed. The extent moisture from normal respiration of the skin, and externally-applied liquids such as water.
Those liquids which normally affect the performance of pressure-sensitive adhesive include body exudations, moisture from normal respiration of the skin, and externally-applied liquids such as water.
Coping with the effect of such liquids has been a primary concern of pressure sensitive adhesive suppliers. In general, it is recommended that an application site (such as the skin) be prepared by cleaning and drying immediately prior to application of the adhesive. For most short duration applications, such preparation is quite effective. However, in many situations, the adhesive device is required to remain adhesively secured to the skin for an extended period of time.
To ensure adequate functionality of the adhesive, suppliers have focused upon two avenues of approach. First, hydrophobic adhesives are employed which are substantially incompatible with those liquids with which they will come into contact. Such adhesives are also designed to be fairly aggressive by nature in terms of the degree of adhesion to the skin. Although effective in anchoring the medical device to the skin, the disruption of skin integrity resulting from attempts to remove the device from contact with the skin can be quite painful and/or irritating to the patient. This is particularly true in those areas where repeated applications to the skin are made, or where the skin is fragile. Any disruption to the integrity of the skin which results can be a significant disadvantage in terms of potential infection, as the protective effect of the skin is compromised.
By way of a second approach, liquid is removed from the skin/adhesive interface. This is accomplished by one of two methods. First, the adhesive device is designed so as to provide a water vapor transmission rate through the device which exceeds the normal respiration rate of the skin. This also assists in reducing maceration of the skin commonly experienced with adhesive medical devices. Such adhesive systems are disclosed in U.S. Pat. Nos. 3,645,835; 4,485,809; 4,452,845; and 4,561,435.
Secondly, a "hydroactive" adhesive composition is employed which is water absorbent. This tends to reduce the moisture content at the skin/adhesive interface, while also reducing the frequency of interfacial failure of the adhesive device.
Unfortunately, if the degree of moisture absorbance is excessive, cohesive failure of the adhesive can result. Tacky or sticky adhesive residue will possibly remain on the skin upon removal of the device, which must then be removed from the skin. Examples of such adhesives are disclosed in U.S. Pat. Nos. 3,339,546; 4,147,831; 4,350,785; 4,393,080; 4,505,976; 4,551,490; and 4,650,817.
Polymeric compositions are also known which are comprised of backbone polymers having grafted thereto pendant polymeric moieties. The type of backbone polymer and graft polymeric moiety employed varies depending upon the desired characteristics of the end product. See, for example, U.S. Pat. Nos. 3,786,116; 3,832,423; 3,842,146; 3,862,077; 3,879,494; 3,928,255; 3,989,768; 4,085,168; 4,551,388; 4,554,324; 4,656,213; 4,693,776; 4,732,808; and 4,871,812 which disclose various types of such polymers which may or may not exhibit pressure sensitive adhesive properties.
Typical of the type of polymeric compositions disclosed in the above patents are compositions comprised of a backbone polymer such as an acrylic or methacrylic backbone polymer having attached thereto a graft polymer comprised of a polymerizable macromolecular monomer such as styrene or alpha-methylstyrene. See, for example, U.S. Pat. No 4,554,324, among others, in this regard.
The acrylic pressure sensitive adhesives such as described in U.S. Pat. No. 4,554,324 may be made from an acrylic ester and a polar acrylic monomer. The polar acrylic monomer can be one or a mixture of acrylic acid, acrylamide, acrylonitrile, itaconic acid, etc. The acrylic ester can be any aliphatic ester of acrylic acid. Such monomers are typically polymerized free radically by solution, suspension or emulsion polymerization. The acrylate portion of the copolymer is generally present in a generally high concentration and renders the polymer tacky. The polar monomer increases the ability of the adhesive to bond to a surface.
U.S. Pat. No. 4,693,776 discloses a pressure sensitive skin adhesive composition comprised of a macromet reinforced acrylate copolymer. U.S. Pat. No. 4,871,812 discloses a moldable medical adhesive comprising a blend of an acrylate terpolymer adhesive containing a hydrophilic macromet moiety, and a reinforcing material which is a carbonylamido group containing polymer. U.S. Pat. No. 4,656,213 is directed to an acrylic hot melt pressure sensitive adhesive comprising a polyacrylate graft copolymer which may be compounded with suitable tackifiers and plasticizers to enhance the adhesive properties thereof. U.S. Pat. No. 4,732,808 is directed to a macromer-reinforced pressure sensitive skin adhesive comprised of a macromet reinforced acrylate copolymer.
Said adhesives have been found to suffer from the disadvantage that their adhesive properties are not sufficiently compatible for use with skin (due to inadequate long-term tack), with the result that adhesive failure may occur after a short time due to movement of the skin.
Further, none of the above patents disclose water-inactivatable pressure-sensitive adhesives which may be readily inactivated once applied to the skin and which exhibit highly desirable tack when applied to the skin.
One solution to the noted problems is described in commonly-assigned U.S. Pat. No. 5,032,637 directed to a pressure sensitive adhesive comprised of a hydrophilic base polymer in admixture with a water-soluble tackifying agent. The base polymer comprises at least one polymer of an alkyl vinyl ether: maleic acid ester in admixture with at least one polyvinyl alkyl ether. The tackifying agent may be, for example, ethoxylated alkyl phenols, glycerol, dipropylene glycol and diethylene glycol.
While the adhesive of U.S. Pat. No. 5,032,637 enables many advantages to be achieved, it is still desirable to provide such a composition wherein the adhesive exhibits enhanced stability under conditions of use.